Catalytic dehydration of glycerol to acrolein over M2.5H0.5PW12O40 (M = Cs, Rb and K) phosphotungstic acids: Effect of substituted alkali metals. (14th December 2016)

• Record Type: Journal Article
• Authors: Hamid, Sharifah Bee Abd; Daud, Nur Atiqah; Suppiah, Durga Devi; Yehya, Wageeh Abdulhadi; Sudarsanam, Putla; Bhargava, Suresh K.
• Is Part Of: Polyhedron. Volume 120(2016)
• Page Start: 154
• Page End: 161
• Publication Date: 2016-12-14
• Subjects: Heteropolyacid catalyst -- Alkali metal substitution -- Glycerol -- Dehydration -- Acrolein; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2016.08.027
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical Abstract: Catalytic conversion of glycerol into value-added chemicals, particularly acrolein via acid-catalyzed dehydration route has received much attention due to the potential uses of acrolein. This work reports the synthesis of various alkaline metal substituted phosphotungstic acid (H3 PW12 O40, HPW) catalysts, namely M2.5 H0.5 PW12 O40 (M = Cs, Rb and K) using a controlled precipitation method. A systematic structural, morphology, and chemical characterization were conducted using various analytical techniques. XRD studies revealed that the incorporation of alkaline metals in H3 PW12 O40 leads to decreased crystallite size and enhanced lattice strain. N2 adsorption–desorption studies show that the specific surface area of H3 PW12 O40 is significantly improved from 5 to 82 (K2.5 H0.5 PW12 O40 ), 103 (Rb2.5 H0.5 PW12 O40 ), and 94 m 2 /g (Cs2.5 H0.5 PW12 O40 ). XRD, Raman, and FT-IR studies confirm the Keggin structure of all the alkaline metal substituted HPW catalysts. The acidity strengths estimated by NH3 -TPD analysis were obtained in the following order: H3 PW (2654.91 μmole/g) > K2.5 H0.5 PW (1060.10 μmole/g) > Rb2.5 H0.5 PW (762.08 μmole/g) > Cs2.5 H0.5.5 PW (461.81 μmole/g). Although alkaline metal substituted H3 PW12 O40 catalysts exhibit higher specific surface area and smaller crystallite size compared to parent H3 PW12 O40 low glycerol conversions were found for substituted H3 PW12 O40 catalysts. As well, the parent H3 PW12 O40 catalyst shows an excellent acrolein selectivity (95%) which is much higher than that of Cs2.5 H0.5.5 PW (81.9%) and very close to the selectivities obtained over Rb2.5 H0.5 PW (95.1%) and K2.5 H0.5.5 PW (95.6%) catalysts. The catalytic performance of H3 PW12 O40 and M2.5 H0.5 PW12 O40 materials is directly proportional to their acidic strengths, indicating that the catalyst acidity is a key factor for achieving better results in glycerol dehydration. Abstract: Catalytic conversion of glycerol into value-added chemicals, particularly acrolein via acid-catalyzed dehydration route has received much attention due to the potential uses of acrolein. This work reports the synthesis of various alkaline metal substituted phosphotungstic acid (H3 PW12 O40, HPW) catalysts, namely M2.5 H0.5 PW12 O40 (M = Cs, Rb and K) using a controlled precipitation method. A systematic structural, morphology, and chemical characterization were conducted using various analytical techniques. XRD studies revealed that the incorporation of alkaline metals in H3 PW12 O40 leads to decreased crystallite size and enhanced lattice strain. N2 adsorption–desorption studies show that the specific surface area of H3 PW12 O40 is significantly improved from 5 to 82 (K2.5 H0.5 PW12 O40 ), 103 (Rb2.5 H0.5 PW12 O40 ), and 94 m 2 /g (Cs2.5 H0.5 PW12 O40 ). XRD, Raman, and FT-IR studies confirm the Keggin structure of all the alkaline metal substituted HPW catalysts. The acidity strengths estimated by NH3 -TPD analysis were obtained in the following order: H3 PW (2654.91 μmole/g) > K2.5 H0.5 PW (1060.10 μmole/g) > Rb2.5 H0.5 PW (762.08 μmole/g) > Cs2.5 H0.5.5 PW (461.81 μmole/g). Although alkaline metal substituted H3 PW12 O40 catalysts exhibit higher specific surface area and smaller crystallite size compared to parent H3 PW12 O40 low glycerol conversions were found for substituted H3 PW12 O40 catalysts. As well, the parent H3 PW12 O40 catalyst shows an excellent acrolein selectivity (95%) which is much higher than that of Cs2.5 H0.5.5 PW (81.9%) and very close to the selectivities obtained over Rb2.5 H0.5 PW (95.1%) and K2.5 H0.5.5 PW (95.6%) catalysts. The catalytic performance of H3 PW12 O40 and M2.5 H0.5 PW12 O40 materials is directly proportional to their acidic strengths, indicating that the catalyst acidity is a key factor for achieving better results in glycerol dehydration.